I was going through some of my older solutions today, and I had to rub my eyes for a second there… Aren’t these two exercises just the same exercise twice with a different name?
Gigasecond was deprecated in favor of Gigasecond Anniversary in Two concepts, 1 exericse: date-time and multiple-values (#509) · exercism/common-lisp@7aa2030 · GitHub so students won’t see both unless they previously solved Gigasecond. It seems the maintainer wanted to use Gigasecond as a concept exercise on the track hence the duplication since it’s normally a practice exercise.
Exactly right. Gigasecond was an exercise for a long time - before the concept/practice split. It makes a perfect concept exercise for dates & times in Common Lisp so it was switched to be a concept exercise (along with the switch from Gigasecond to Gigasecond Anniversary)